This invention relates to an improved method and apparatus for molding a dental prosthesis in situ.
It has previously been known to form a temporary prosthesis for the restoration of defective teeth in a patient's mouth by forming the temporary prosthesis directly in the patient's mouth. Such method first requires the formation of a negative impression of the patient's mouth before preparation of the teeth to receive the prosthesis. Then, the teeth are prepared by cutting them down as necessary and attending to various undercuts, etc. A cold adhering acrylic resin mixture is formed into a dough-like consistency which is then packed into the negative impression in the area to be restored. The negative impression, now with the mass of acrylic resin, is then inserted in the patient's mouth over the prepared teeth. The acrylic resin is allowed to cure in the mouth. The negative impression is them removed leaving the cured acrylic resin over the teeth. Finally, the cured acrylic resin is also removed from the mouth, trimmed off and formed as a temporary restoration.
This method has numerous problems, mainly because of the required use of the dough-like mass of acrylic resin formed in the patient's mouth. Frequently, the material squeezes out between the impression and the mouth forming a flash around the restoration. The flash produces many problems including flowing over adjacent teeth and tissue, preventing the impression to be fully seated in the mouth, requiring further recontouring of the restoration and exerting hydraulic pressure against the contour of the flexible impression material deforming the surface of the prosthesis. Additional problems of using the dough-like acrylic resin are well known.
Because of these problems, the aforereferenced patent application provided an improved method of forming a dental prosthesis in situ in the patient's mouth. The method of the referenced patent includes the formation of an elastomeric mold half over a positive model of the patient's jaw in the area where tooth restoration is required. The mold is formed with overlapping boundaries of the tooth area to be restored in all directions by a predetermined distance. Two holes are drilled through the elastomeric mold at opposite ends of the mold cavity. Tubular fittings are applied to each of the holes and connect to flexible tubes. One of the tubes is a flexible exhaust tube having a filter therein, while the other tube is a flexible inlet tube. The patient's teeth are then prepared for the restoration including the cutting down of selected teeth. The elastomeric mold half is then placed back onto the patient's mouth over the tooth areas prepared for restoration with the free ends of the flexible tube leading outside of the mouth. The free end of the exhaust tube is connected to a vacuum pump while the free end of the inlet tube is connected to a receptacle containing a mix of self-curing liquid resin, and especially acrylic resin. With the inlet tube clamped, a predetermined vacuum is then formed in the mold cavity. The elastomeric mold is thereby sealed around the patient's mouth so that the vacuum is maintained within the mold cavity. After the vacuum is achieved, the inlet tube is opened whereupon atmospheric pressure acting on the liquid resin in the receptacle forces the liquid resin through the inlet tube into the evacuated mold cavity. The liquid resin is allowed to cure until solid and then the elastomeric mold removed.
The formation of the dental prosthesis in accordance with the aforereferenced patent application presents numerous advantages as is described therein. However, one of the problems with that method is that the prosthesis is formed directly in the patient's mouth. This requires keeping the patient still with various dental machinery attached to his mouth for long periods of time. Specifically, during all the time that the vacuum is formed, the seal is tested, and the acrylic liquid resin is flowing in and curing, the patient must remain in position with his mouth open while supporting all of the various dental machinery. This becomes quite burdensome. Additionally, since the vacuum is formed directly in the patient's mouth between the inner surface of the elastomeric mold and the outer surface of the prepared teeth, there must be provided sufficient overlapping of the elastomeric material to form the seal directly in the mouth. This requires larger elastomeric molds and more discomfort to the patient. Also, it requires that the seal be tested until a proper vacuum is supported within the mold cavity. This may mean repeated attempts until such time as a proper seal is formed between the elastomeric mold and the patient's mouth. Furthermore, the apparatus of the system includes pumps, tubing, clamps, etc. all of which must be supported adjacent the patient's mouth which makes for a complex procedure.
The solution to these problems would be to form the temporary prosthesis externally of the patient's mouth utilizing a mold cavity formed between the elastomeric mold and a stone model of the patient's teeth. However, the process of the aforereferenced application is dependent upon the forming of a seal between the two halves of the mold cavity whereby the mold cavity itself must be capable of maintaining the vacuum. In the aforereferenced application, the mold cavity is formed between the elastomeric mold half and the patient's mouth and a seal must be provided between them so that a vacuum can be maintained within the cavity.
As a result, the aforementioned process of the referenced application could not be used on a stone model of the patient's teeth because a vacuum seal could not be made between the elastomeric mold half and the stone model. As is known, a stone model is not dense enough to prevent leakage of air between the two mold halves. As a result, any attempt to maintain a seal between them and have the mold cavity formed between the elastomeric mold half and a stone model to support the vacuum would not be feasible.
A possible solution would be to form a partial vacuum in such cavity between the elastomeric mold and the stone model and maintaining such partial vacuum by continuous pumping of the vacuum pump thereby forming a continuous evacuation of the cavity. The pump would, of course, have to have sufficient capacity to pump out sufficient volume so as to overcome the air coming into the mold cavity as a result of the leakage. However, the continuous pumping necessary to evacuate such a mold cavity would be centrary to the principles of the technique of the invention. The technique is dependent upon forming a "static" vacuum i.e., where no pumping is carried out while the material is being introduced into the mold. Specifically, the static vacuum is formed by first clamping the inlet pipe while a vacuum is produced in the mold cavity. then, after the formation of the vacuum, the clamp is released whereby atmospheric pressure pushes the liquid resin into the mold cavity. Utilizing continuous pumping would pull the material into the mold cavity. The static vacuum of the invention allows the material to be pushed into the mold which provides the improved prosthesis desired.